The new Baldur's Gate - Descent into Avernus hardcover features a brand new mechanic: Infernal War Machines! A few things caught my eye - first off, that they have a stat block:
An infernal war machine's statistics function like those for creatures
Then, that their opportunity attack mechanics function a lot like those of mounts:
Infernal war machines provoke opportunity attacks as normal. When an infernal war machine provokes an opportunity attack, the attacker can target the vehicle or any creature riding on or inside if that doesn't have total cover and is within reach.
Also, that their driver can control their movement much like a mounter controls a (non-intelligent) mount's movement:
While the vehicle is moving, the driver can steer it along any course.
And that they can make the vehicle Dash/Disengage (in a similar but different manner that a mounter commands a mount to do so):
As a bonus action, the driver can do one of the following: […] Cause the infernal war machine to take the Dash or Disengage action while the vehicle's engine is running.
In summary, Infernal War Machines seem similar, in certain points at least, to mounts. What I'm wondering here is: how would a driver with the Mounted Combatant feat interact with these Machines? Would the feat's benefits work with the Machines or not?
Reminder on the Mounted Combatant feat:
You are a dangerous foe while mounted. While you are mounted and aren't incapacitated, you gain the following benefits:
- You have advantage on melee attack rolls against any unmounted creature that is smaller than your mount. You can force an attack targeted at your mount to target you instead.
- You can force an attack targeted at your mount to target you instead.
- If your mount is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.
From a thematic standpoint, I think it would make sense for a specialized "Helldriver", so to speak, to gain benefits from that feat while driving an Infernal War Machine, but actual-mechanics-wise, I am unsure.